1. Field of the Invention
The present invention relates to a variable valve operating device for an engine to adjust an opening and closing timing and a valve lift amount of an intake valve and an exhaust valve provided in the engine. More particularly, the invention relates to an adjusting device of a valve lift and a valve timing of an engine in which a valve timing cannot be adjusted during a valve-opening period of the intake valve, the exhaust valve, and the like, and the valve timing can be adjusted during a valve-closing period thereof.
2. Description of the Related Art
As a conventional configuration for opening and closing an intake valve and an exhaust valve provided in an engine, it is general to apply a rocking motion to a rocker arm by a cam provided on a rotatable cam shaft, and to push valve tappets of the intake valve and the exhaust valve by a tip end of the rocker arm, thereby opening and closing the intake valve and the exhaust valve. As a configuration for adjusting the valve lift and the valve timing corresponding to an output of the engine, a configuration for adjusting a lever ratio by moving a fulcrum of the rocker arm is employed (For example, see Patent Document 1: Japanese Patent Application Laid-Open No. S64-53009 and Patent Document 2: Japanese Patent Application Laid-Open No. H6-74011).
According to the configuration for adjusting the valve lift and the valve timing in the Patent Documents 1 and 2, a rocker arm which is rocked by a cam of a cam shaft to open and close the intake valve and the exhaust valve, and a fulcrum of a rocking cam are moved to change and adjust the lever ratio. However, this is not a configuration in which the fulcrum is fixed when the intake valve and the exhaust valve are opened and the fulcrums can be moved when the valves are closed.
When the intake valve and the exhaust valve are opened, it is necessary to fix the rocker arm and the fulcrum of the rocking cam so as not to move so that the intake valve and the exhaust valve can be opened in a stable state. To enhance the responding speeds of adjustments of the valve lift and the valve timing, it is desirable to adjust the movement of the fulcrum when the intake valve and the exhaust valve are closed.
Hence, one approach is to configure a lock unit that locks the fulcrum of the rocking cam and the like so as not to move at the time of opening the valves using a retarder that uses a solenoid. However, it is necessary to demagnetize the retarder when the fulcrum is unlocked thus requiring control thereof and time therefor, which becomes a problem in enhancing the responding speed.